1. Field of the Invention
The invention relates to stepper motors. More particularly, the invention relates to a resonant circuit control system designed to effectively conserve energy during the operation of a stepper motor.
2. Description of the Prior Art
The use and theory of stepper motors are well developed. The term "stepper motor" is known to describe, but is not limited to, switched reluctance motors, variable reluctance motors, electronically commutated reluctance motors, variable reluctance stepper motors, brushless DC motors, and other forms of stepper motors. Stepper motors may have a bipolar or unipolar construction. Bipolar motors have a rotor constructed using permanent magnets and unipolar motors have a rotor constructed of soft iron materials (or related materials) that respond to the magnetic field produced by the stator.
The general operating principle of a stepper motor relies upon a winding mounted on a stator to conduct or block current based on the position of the rotor. As such, stepper motors are generally constructed without the brushes commonly found in electric motors. In place of brushes, the stepper motor depends on switches to control the flow of electrical charge through a particular phase winding. Stepper motors advantageously offer the ability to control the exact increment of motion, or the change in a rotor angle, by the use of a control system. Each winding relates to a specific phase and each phase to a specific increment or angular change from the previous phase. This incremental change in angle is referred to as a "step", hence the general description of this family of devices as stepper motors.
Prior art stepper motors have been designed with resonant systems for driving the motor. However, no prior art stepper motors have been disclosed which use capacitors to efficiently capture and recycle most of the charge passing through a winding.
With reference to the control system disclosed in FIG. 1, a two winding system for a bipolar stepper motor 1 is disclosed. In operation, the first switches 2a, 2b are turned on (all other switches are not conducting) and electrical charge flows through the first winding 3 in the forward direction as indicated by the arrow. This produces the first phase of the stepper motor sequence. The second phase is produced by turning the third switches 5a, 5b on (all other switches are turned off) to energize the second winding 6 with electrical charge flowing in the noted forward direction. The third phase is produced by turning on the second switches 6a, 6b while all other switches are off. This allows electricity to flow in the reverse direction through the first winding 3. Finally, the fourth phase occurs when all switches are turned off except the fourth switches 7a, 7b, allowing the second winding 6 to be energized with electrical charge flowing in the reverse direction.
This conventional arrangement of switches and windings in a bipolar stepper motor is referred to as an H-bridge (where the winding is the cross member of the H and the switch circuit composes the uprights). The current flow through the switches of the H-bridge are unidirectional and the current flow through the winding is bidirectional (hence the quote bipolar stepper).
The phase process is repeated with the rotor of the stepper motor turning a discrete amount for each phase. The stepper motor is locked or held in position by leaving one phase active. In the case of holding or locking, the current flowing through the winding exerts a given magnetic force on the permanent magnets in the motor to produce a holding torque. If the phases are switched too slowly, the stepper actually locks momentarily (achieves holding torque) in each phase, causing a jerking motion often accompanied by a clicking sound.
The prior art control systems, however, expend substantial energy in cycling through the many phases. As such, a need exists for a more efficient control system to be used in the operation of unipolar and bipolar stepper motors. The present invention provides such a control system.